This invention relates to a method of dissolution of pyrotechnic materials containing cured or crosslinked organic polymers as binders.
Every year, large amounts of pyrotechnic materials must be disposed of due to deterioration or obsolescence. In the past, pyrotechnics have been disposed of by dumping them in the ocean, burning them in an open area, or detonating them in a safe zone. Viewed from an ecological standpoint these methods are undesirable because they contribute to contamination of the ocean and to pollution of the atmosphere by releasing corrosive hydrogen chloride gas and noxious oxides of nitrogen into the air. Because of concern over minimizing all sources of environmental pollution, the need exists for an ecologically sound alternative method for disposing of unwanted pyrotechnic materials.
In addition to being inexpedient from an ecological standpoint, the previous methods of disposal are unsatisfactory from an economic point of view. The utter waste of valuable raw materials which are used in the preparation of pyrotechnic materials is readily apparent when methods such as those mentioned above are employed for the disposal of these items. Accordingly, it would be desirable to develop a process whereby some or all of the components which make up the pyrotechnic materials could be recovered and reused.
Several methods have been proposed in the prior art for the decomposition of polymeric materials. One such method involves heating polyurethanes in the presence of the polyol used to prepare the original polymer, as disclosed by Ten Broeck in U.S. Pat. No. 2,937,151. Other methods involve heating polyurethanes in the presence of a primary amine, as disclosed by McElroy in U.S. Pat. No. 3,117,940, or heating polyurethanes in the presence of an amine in combination with a strong base, as disclosed by Matsudaira et al in U.S. Pat. No. 3,404,103. More recently, Frulla et al have described a process for the decomposition of scrap polyurethane foam by heating in the presence of a mixture of an eliphatic diol and a dialkanolamine. Some of the above described prior art methods do not provide for recovery of the chemical components of the decomposed polymeric material, while others utilize some combination of high temperature, high pressure or high alkali concentration, which conditions are not compatible with the recovery of pyrotechnic materials components due to their instability.
Tompa et al in U.S. Pat. No. 4,098,627 disclose methods by which a pyrotechnic material containing a cured polymeric binder is decomposed under much milder conditions so that many of the starting materials can be recovered. The method involves heating the pyrotechnic material to a temperature of from about 50.degree. C. to about 160.degree. in a liquid medium comprising an active hydrogen containing compound capable of cleaving the chemical bonds contained in the polymeric binder. One or more of the products resulting from the decomposition of the pyrotechnic material can be separated and recovered. The active hydrogen containing compounds included primary amines, secondary amines, ammonia, mineral acids and water. Unfortunately, the alkaline processes (amines and ammonia) destroyed any nitramines present. The use of mineral acids and water resulted in some recovery of nitramine, but the yields were very low (e.g., 36%). Because nitramines are expensive it would be desirable to find a method of recovering them in high yield (i.e., 80% or more).